1. Field of Invention
This invention relates to vehicle suspension systems, specifically for attaching a rigid axle of the vehicle to it's frame, chassis, or body by way of multiple, pivotal, connecting links, arms, tubes, bars, etc. to stabilize the axle in fore, aft, and rotational directions.
2. Description of Prior Art
It is well known, one method to attach a rigid axle, either powered or not, to the frame, chassis, or body of a vehicle is by using a four-link type of connecting arm suspension to stabilize an axle against forces acting on it in fore, aft, and rotational directions.
The four-link suspension comprises four axle to frame connecting links. One end of each link is pivotally attached to the frame, chassis, or body of the vehicle and the other end of each link is pivotally attached to a rigid axle of the vehicle. Two link ends are pivotally attached above the axle centerline and two link ends are pivotally attached below the axle centerline.
The problem of nearly if not all four-link suspensions is that in order for a vehicle to lean from side to side, or traverse a bump, or incline a surface at an uneven angle, the two connecting links above the axle have to be mounted at an essentially parallel angle to the two connecting links below the axle, and all links need to be of equal length in order for the suspension to not bind up. When a four-link suspension binds it means one end of a rigid axle cannot move up or down independently of the other end. Incidentally many vehicle's chassis or bodies do not enable the use of parallel and equal length axle connecting links.
In addition, the consequences resulting from a suspension that continually binds can be dangerous. Especially in heavy equipment and racing applications,suspension bind creates undesireable stresses on the suspension components leading to fatigue,fracture, and eventual failure of suspension parts, attaching bracketry, or framework of the vehicle.
Most vehicle manufacturers, primarily of automobiles, alleviate this problem of suspension bind by utilizing large rubber or elastomeric bushings at all connecting link ends. Thus, allowing one end of an axle to move up or down within a very limited range of the other end, but at a high deformation rate and relatively short life span of the rubber or elastomeric bushing.
Heavy duty vehicles and racing vehicles are subject to much more severe loads and forces acting on the vehicle chassis. The application of elastomeric bushings or bearings on these type of vehicles is just about nonexistent.
Many automobile and truck,high performance and racing,suspension designers and chief mechanics like to experiment with different angles and lengths of the frame to axle links, in order to get the vehicle to react and handle better under acceleration, deceleration and braking, cornering, and bump forces. But, the problem of suspension bind can then be manifest especially in the four-link type suspension.
To solve this problem of suspension bind and be able to use a suitable bearing of a less deformable or compressable material than an elastomer at the link ends (optimumly bearings made of a metal or alloy) the three -link suspension was conceived.
The three-link suspension has no bind whatsoever when one end of a rigid axle is moved up or down without the other end doing the same, while utilizing spherical rod end bearings at all connecting link ends. Such bearings commonly made out of steel, or other metal, or an alloy, or combination.
The three-link suspension is like the four-link except, for example, of the upper pair of links, one link is omitted and the other link is usually relocated between the lower pair of links laterally extending in the direction lengthwise of the vehicle and now becomes the single upper link.
Some problems with the three-link suspension are that it is generally not as strong, as safe, or as versatile with regards to setup of angles, degrees of incline, or chassis and axle mounting locations of the links, as the four-link is.
Often it is not possible to mount a third link near the lateral center of a vehicle as there likely wont be a sturdy section of the chassis to accept a bracket for the third link attaching end. Especially, when considering a high torque or horsepower engine transmitting power to the axle.
Another drawback of the three-link suspension, when applied to a powered axle, is the lack of adjustability becomes apparant as the driveshaft needed to transmit power to the axle is usually in the way. Thus, making it difficult to position the third link in anyway other than generally parallel the longitudinal axis of the vehicle due to driveshaft interference.
Furthermore,when closely observing the average production automobile that is equiped with a rear seat, it becomes quite obvious that there is no room to mount a third link because the rear seat is taking up the space.
To be more specific about the three-link and four-link suspensions as applied to the typical automobile or truck which utilize a rigid rear drive axle. These vehicles incorporate a front mounted engine with attached transmission connected by way of a driveshaft to a rigid rear drive axle. When attaching this rear drive axle to the vehicle chassis it becomes necessary to point out that a pair of the connecting links of either the three or four-link type of suspensions are usually located with one link near each end of the axle, and both links being on the same horizontal plane, either above or below the axle centerline. This pair of connecting links when set up in the vehicle's suspension should be positioned parallel to the level ground and normally parallel to each other as well. This is to insure neutral steer of the rear axle to make for a more predictable and stable vehicle to control in high-performance cornering or high-speed driving situations. Thus, the other one link in a three-link or two links in a four-link system are all that is left to make suspension setup and tuning adjustments.
Now to show an example of usually automobiles in particular. To leave the bottom pair of links roughly parallel to the ground and vehicle longitudinal axis is what works well for most automobiles due to chassis or body mounting locations or clearance considerations. This becomes apparant when looking at the first embodiment of the invention.
To set the remaining link(s) at a variety of angles pointing downward from the top of the rear axle toward the bottom of the chassis, forward of the rear axle, is the essence of suspension setup and tuning adjustments for most sports car and race car applications. Any of the various angles from parallel the bottom links to the highest degree feasible of the downward angle of the upper link(s) is what is normally desireable. Rarely if ever is (are) the upper link(s) pointed in an upward direction from the top side of the rear axle, as reasons to follow in the next paragraph.
The higher the degree of downward angle of the upper connecting link(s) serves one probably two purposes: 1) lessens wheel hop of the rear tires under hard acceleration, due to the torque of the powered rear axle pulling up on the vehicle chassis and thereby planting the rear tires harder on the ground; and 2) theoretically under hard braking, deceleration forces acting on the rear axle allows the reverse torque generated to press down on the vehicle chassis thereby reducing the amount of rear body lift while slowing down, thus making for a shorter stopping distance and less chance of rear wheel lockup or skid.
Now apply the limitations of the three-link and four-link suspensions as previously described, and we're back to square one. Therefore, a solution is needed that would overcome the shortcomings of the two before mentioned types of rigid axle link attached suspensions and many other types not mentioned as well.